Autogenous chondrocyte transplantation has been used to treat the chondral defect since 1994, comprising collecting chondrocytes from normal cartilage tissues, expanding these cells in a medium in vitro as much as possible, and then filling the chondral defect by implanting the expanded cells in artificial scaffolds. However, there are still many problems; for example, the source of autogenous chrondrocytes is limited, the proliferation ability of chondrocytes is low, and their unique phenotypes may be lost during expansion (Saadeh et al., Human cartilage engineering: chondrocyte extraction, proliferation, and characterization for construct development. Ann Plast Surg 1999; 42:509-13).
Mesenchymal stem cells (MSCs) are able to differentiate into cells of connective tissue lineages including cartilage and thus becomes an attractive cell source for cartilage tissue engineering. Many methods have been used in chondrogenic induction of MSCs. Kavalkovich et al. provided a pellet culture method mimicking the environment of embryonic cartilage development, wherein a high cell density of cells were obtained but a tightly aggregated cell mass with a large amount of cells forming only a small volume of chondral tissue was present. Therefore, a considerably large number of the cell pellets were required for repairing a defective cartilage, and the large pellets exhibited a periphery of viable cells, but the pellet center became necrotic (Kavalkovich et al., Chondrogenic differentiation of human mesenchymal stem cells within an alginate layer culture system. In Vitro Cell Dev Biol Anim 2002; 38:457-66.). In addition, pellets are difficult to handle and to mold into various shapes needed for defect repair. Given the above, the pellet culture is impractical for surgical applications. Furthermore, it was found that embedding human MSCs (hMSCs) in agarose or alginate gels could be cast into various shapes and caused substantial chondrogenesis (Huang et al., Chondrogenesis of human bone marrow-derived mesenchymal stem cells in agarose culture. Anat Rec A Discov Mol Cell Evol Biol 2004; 278:428-36; and Ma et al., Chondrogenesis of human mesenchymal stem cells encapsulated in alginate beads. J Biomed Mater Res A 2003; 64:273-81). However, the alginate or agarose scaffolds for cartilage tissue engineering have the drawbacks: poor cell adhesion, and uncontrollable degradation of alginate following the diffusion of divalent cations into the surrounding medium. In addition, alginate matrices were used in the in vivo applications and reported to have severe foreign body giant cell reactions and immunological responses when implanted to treat full-thickness defects in cartilage in experimental animals (Hunziker, Articular cartilage repair: basic science and clinical progress. A review of the current status and prospects. Osteoarthritis Cartilage 2001; 0:432-63). Hence, alginate matrices have not been employed in human patients for articular cartilage repair.
Therefore, it is still desired to develop a surgical graft for repairing a chondral defect in a patient.